Slot machines are popular gaming machines in casinos. There are many types of slot machines and some of the slot machines, which may be referred to as mechanical slot machines or stepper machines, have mechanical reels each bearing a series of symbols thereon. Other slot machines, which may be referred to as video slot machines, have a display for displaying a plurality of cells or columns in which symbols (or indicia) are shown randomly in each game. When the symbols shown by the reels of the mechanical slot machines or shown in the cells or columns of the video slot machine form one or more winning combinations, a corresponding award is paid to the player.
Also, recent slot machines typically have a secondary game in addition to the primary game (or slot game). The secondary game is often called a bonus game and is initiated upon the occurrence of a selected event or outcome of the primary game, or may be triggered by a separate event that may or may not be connected to the primary game. For example, the secondary game may be triggered based on a random number generated by a random number generator separately from a random number generated for determining the outcome of the primary game.
The secondary game may include any type of game, either similar to or completely different from the primary game. For example, the secondary game may be embodied as a progressive game. As is well known in the art, in the progressive game, an award (“progressive award”) paid out to the player consists of an award that has been updated or increased by accumulating a portion of the player's bet of the primary game. Typically, the progressive award comprises several levels having different reset values, on which the portion of the player's bet is accumulated. When a predetermined condition for winning the progressive award is met during a primary game, the progressive game is triggered to determine at least one of the several progressive levels that is paid out to the player as the award, and the value of the paid out progressive level is reset to its reset value. As mentioned above, the predetermined condition may be related to the outcome of the primary game or may be based on a selected event that may not be related to the outcome of the primary game.
There are many examples of the progressive game of the gaming machine. One of them is disclosed in U.S. Patent Application Publication No. 2009/0143133. The gaming device related to this patent application publication is designed such that the gaming device enables an average investment necessary to win the progressive award (or jackpot) to be uniform by varying odds of winning the progressive award as the player's bet varies. That is, a player betting less money needs to play the game for a longer time, in general, to win the jackpot Likewise, a player betting more money can reach the condition to start the progressive game to win the jackpot in a shorter time, in general. The average overall bet or investment thus remains constant despite the player's betting habits or betting ability.
As described above, the odds of winning the progressive award or a hit frequency for triggering the progressive game is determined based on a player's bet amount in the above conventional gaming device such that the average overall bet or investment necessary for winning the jackpot remains constant. That is, in order to maintain the average investment for winning the jackpot to be constant (for example, $200), the higher the player's average bet becomes (for example, $200/minute), the higher the hit frequency for triggering the progressive game becomes (for example, one time per one minute). Likewise, the lower the player's average bet becomes (for example, $0.5/minute), the lower the hit frequency for triggering the progressive game becomes (for example, one time per 400 minutes). Therefore, these conventional progressive systems have a problem that the hit frequency for triggering the progressive game can drastically change to such a degree that the hit frequency can be impractically high or low depending on the player's average bet. Especially, in a linked progressive system where a lot of gaming machines are connected so that a portion of the bets on these gaming machines is accumulated on the progressive levels, the hit frequency for triggering the progressive game may change even more drastically because the occupancy rate can change in a wide range throughout a day or a week and this significantly affects the average bet per game by the players. This problem is inherent in conventional math model and has not been solved so far. The present invention is aimed at one or more of the problems set forth above.